1. Field of the Invention
The production of cheese generally involves the steps of clotting or coagulating milk to form a curd, cutting the curd into pieces and cooking the curd. The cooked curd is then separated from residual whey, mixed with salt, and pressed and cured to form the desired cheese product. In the classical method of making cheese, rennet, an enzyme-containing preparation obtained from the fourth stomach of milk-fed calves, is used. Since rennet is derived from calves, the quantity of rennet available for cheesemaking is directly dependent upon the number of calves that are being processed for food purposes. This has prompted attempts in the prior art to develop suitable microbial enzyme preparations ("microbial rennets") to serve as substitutes for calf rennet. Several microbial rennet preparations have been developed. These are prepared, for example, from Mucor pusillus and Mucor miehei.
Enhancement of the milk coagulating activity of microbial rennet has been a continuing goal of research efforts.
2. Prior Art
Belgian Pat. No. 880870 claims a method for reducing the thermal stability of microbial rennet by acylating the rennet with a monocarboxylic acid acyl radical having from 1 to 6 carbon atoms. The applicant notes that during the cheesemaking process, the whey is recovered and pasteurized and utilized, e.g., as an additive to whole milk, to produce enriched milk. If the microbial rennet is thermally stable, pasteurized whey may still contain a level of proteolytic activity sufficient to produce undesirable protein coagulation.
The patentee of the Belgian Pat. No. 880870 acknowledges that acylation produces a loss of milk coagulating activity and places great emphasis on the importance of thermal destabilization over the importance of the coagulating activity of the microbial rennet produced. The patentee indicates that a destabilization of from 3.degree.-5.degree. C. with a coagulating activity loss up to 50 percent seems to be an appropriate compromise between the above-mentioned conflicting factors.
U.S. Pat. No. 3,886,042 describes the modification of proteolytic enzymes to increase the hydrolase activity by acylating with an acylating agent containing an amino acid residue, e.g., acetylalanyl, acetylphenylalanyl and .beta.-phenylpropionylphenylalanyl. The patent does not disclose any data relating to milk coagulating activity.
The present invention discloses and claims a method of acylating microbial rennet obtained from Mucor pusillus with selected anhydrides whereby the milk coagulating activity of the enzyme can be increased over 100 percent. Neither of the above-referred-to patents disclose or suggest a method of increasing milk coagulating activity.